1. Field of the Invention
The present invention generally relates to measurement technology and more specifically to magnetizers for magnetic inspection of articles and is aimed at magnetic recording of flaw margins in the course of magnetic flaw detection, e.g., in the case of quality inspection of intricately shaped ferromagnetic components or of some individual surface areas thereof.
2. Description of the Prior Art
One prior art magnetizer is known to comprise a number of series-connected electromagnets. Such a device enables magnetization of a rather long section of a weld seam on which magnetic tape is applied, but fails to establish a homogeneous magnetic field within the zone of the welded joint. Besides, magnetic tape induces additional distortions developed when magnetograms are decoded, this being due to the fact that when there is a variable profile of the surface under inspection, e.g., in the case of a weld reinforcement, the magnetizer fails to provide a uniform magnetic flux within the zone of the magnetic tape. Moreover, it is a difficult task with the known magnetizer to attain magnetic tape operation on the linear portion of its B-H curve (cf. USSR Inventor's Certificate No. 214,869, Class 42 K 46/03 published in 1968).
Known in the present state of the art is another magnetizer for magnetographic inspection of articles, comprising a main electromagnet, an auxiliary electromagnet (of lower power as compared with the main electromagnet) interposed between the poles of the main electromagnet in the central zone of the magnetic field thereof in such a manner that the intrinsic magnetic field of the auxiliary electromagnet is capable of interacting with the field established by the main electromagnet, and a power supply unit for the windings of the electromagnets (cf. USSR Inventor's Certificate No. 418,786, Class G OI N 27/82 published in 1974).
The auxiliary electromagnet provides for establishing of an additional magnetic flux in the zone of the article being magnetized with the main electromagnet, the additional magnetic flux correcting the component of the main magnetic field in this zone, which is the case with, e.g., weld inspection when the additional magnetic flux is to correct the main electromagnet magnetic flux component within the weld zone, said component being closed through the weld bead.
However, there exist a great number of articles (e.g., intricately shaped heavy-weight sturdy items such as diesel-engine framework, various beds and frames, butt-joints of pipes featuring different wall thickness, and the like), wherein apart from the presence of a weld seam within the zone under inspection, there are also such specific features as an intricate profile of the article itself and variable thickness across the zone under inspection. This leads to leaks of the magnetic flux into the heavy cross-section zone of the article in the course of magnetographic inspection, as well as to inhomogeneous magnetic flux, adversely affected sensitivity of the inspection method and hence makes it impossible to provide magnetic tape operation on the linear portion of its characteristic (B-H) curve. All this results in failure to detect some flaws, e.g., such hard-to-reveal ones as dissimilarly oriented defects, or introduces errors in determination of the size of a defect.